Embossing: high frequency loss in inner grooves

[basplin]

Hi all - reaching out for some help with a strange issue I've encountered in my embossing learning. I have a ROK M5 with a Presto 1D and I'm learning to emboss with a sapphire stylus. I'm starting to get some great results but I'm realizing that as I cut inwards, I'm losing high frequency response, maybe all the way down to 10K? in the very inner grooves. This is a contrast to the outer grooves I'm cutting which are up to 15K. I can rule out the head because I've done back to back cuts on the outside and inside and still get the very noticeable high range loss on the inner grooves. The only thing I can think of is that the overhead is pushing down more on the spindle with the weight of the carriage as it moves in, thus maybe bending the record slightly, but I haven't been able to observe this. Anyone else ever have this issue? Any other ideas what could be causing it? Or is this just a limitation of embossing? (Seems like a big one if so). Thanks!
Ps- apologies if this has already been brought up! I’ve tried searching with different key words but couldn’t come up with anything. Feel free to just post the thread if this has been mentioned elsewhere...thanks!

[Aussie0zborn]

There is a natural high frequency loss in disc recording with each revolution. As you get to smaller diameters you are trying to cram more information into a shorter space.

The circumference of a 12” disc is nearly 38 inches. At 33.3rpm that gives you 38” to record 1.8 seconds of music.

The circumference at 7” is nearly 22 inches so now you’re cramming that same 1.8 second of music into just 22”.

Even so, a drop from 15kHz to 10kHz seems quite high. Somebody with embossing experience might be able to shed some light on the subject.

[basplin]

Thanks for the reply! I should have mentioned that that was also a consideration... is that something that differs with embossing from cutting? I know there is loss in fidelity as you cut inwards, but not that kind of loss in HF. Playing records I notice the sound just tends to get kinda grainy.

[markrob]

Hi,

In addition to diameter loss, there is the fact that when you emboss, there is a self erasure of detail since the embossing tool cross section is circular. Whereas, a standard cutting stylus approaches a single point tool. Diameter loss is a playback phenomenon due to the geometry of the pickup stylus being unable to trace the details cut by the stylus. When Embossing high frequencies, the loss happens at the time of cutting. You can improve things by making the embossing tool smaller in diameter, but at some point you will transition from embossing to cutting. Cutting at 45 or 78 vs. 33 will also help on both fronts. See the copy of the paper on this topic attached.

Mark

[fredbissnette]

Hook up some kind of external three band eq and turn up the highs as you get close to the center

[basplin]

Mark - this is great, thanks for sharing!
Fred - I actually just had this idea last night. I'm planning on getting a 31 band EQ so I could just use one of those

[fredbissnette]

the 10k slider will be your friend

[EposLab]

The only thing I can think of is that the overhead is pushing down more on the spindle with the weight of the carriage as it moves in, thus maybe bending the record slightly, but I haven't been able to observe this

As long you the platter is flat then i dont think is problem. Be sure to balance your overhead carefully so the cutter will apply equal cutting cutting force all the way in. I found this to be the most important. Although i have the "same" B-5 overhead and 1-D cutter (mod by agnewanalog) i can cut flat to 12k (at the outer of the 12") using a tungsten stylus and windth of 2mil. I have tried the sapphire which extends abit more but is far more noisier and i really dont like that.


Ps. @markrob thanks for sharing !